The present invention relates to a sheet composed of multiple films for producing peel-off lids of containers made of plastics with preset opening by tearing of at least one film.
Sheets constituted by the mating of composite films that can be separated because of the reduced resistance to separation provided between two preset layers in contact are already known.
Containers for food products, such as yogurts, fruit juices, et cetera, with lids formed by means of such composite sheets are also known and achieve, upon separation by peeling of the external composite film, tearing of a preset region that gives access to the container in order to be able to extract the contained product.
As mentioned, these containers are mostly used in the food industries, and it is essential to comply with strict hygiene rules.
Accordingly, in normal conditions there must be no possibility of deterioration of the contained product.
Deterioration can occur for various reasons, such as the actions of ultraviolet rays, contamination with microorganisms, and intake of oxygen from the environment.
All these causes of deterioration are due to the structure of the composite sheet, which does not provide the certainty of forming an assured barrier.
EP-812,782 discloses a sheet composed of multiple films for lids of containers, which can be opened by peeling off one film with respect to another and in which during opening a pre-scored portion of the film is removed and remains attached to the container, exposing a hole.
Due to the above cited hygiene requirements, the pre-scored portion should not be of the through type, but this characteristic, owing to the low thickness of the layers involved, is not ensured, and any through holes, even if small, make the layer of film of the pre-scored region ineffective as a barrier.
The aim of the present invention is to provide a composite sheet for forming peel-off lids of containers made of plastics with preset opening that eliminates the drawback noted above in known types of sheets.
Within this aim, an object of the invention is to provide a sheet whose peelable part allows its easier separation with respect to the rest in order to make the container opening operations convenient for the user.
Another object is to provide an assured barrier against contaminations of the product contained in the container to which the sheet is applied.
Another object is to provide a composite sheet that can be manufactured with conventional equipment and systems.
Another object is to make attempts to tamper with the opening automatically evident.
This aim and these and other objects that will become better apparent hereinafter are achieved by a sheet composed of multiple films for providing peel-off lids of containers made of plastics with preset opening, characterized in that it comprises:
a first set of films, comprising a film constituted by a layer of aluminum or equivalent material, coated externally with a film of polythene and coupled inward, by means of an adhesive, to an orientated last plastic film;
a second set of films, the last one being heat-sealed to the edge of a container to be closed, said second set of films comprising a pre-perforated first orientated plastic film that is coupled, by means of an adhesive, to a non-perforated polythene film that is heat-sealed to said edge of the container;
a hot-extruded polythene layer being interposed between said two film sets and rigidly coupling the last orientated plastic film of the first set of films and the first orientated plastic film of the second set of films, penetrating furthermore between the holes of the first orientated plastic film of said second set and being heat-sealed to the polythene film of the second set of films, which is the last film and is heat-sealed to the edge of the container.